Currently, two principal methods are employed industrially for the synthesis of methyl halides. One method involves the chlorination of methane and the other relies on the reaction between methanol and a hydrogen halide. The latter process is the most widely employed and accounts for most of the methyl chloride production in the world. This method produces methyl halide as the sole product of reaction whereas the halogenation of methane typically yields mixtures of methyl halide, methlyene halide, haloform and carbon tetrahalide.
Both of these procedures, however, require the utilization of relatively high temperatures and, typically, high pressures, to achieve acceptable yields. These rigorous reaction condition requirements necessitate the use of expensive equipment and not infrequent shut-downs for repair and replacement thereof due to the deleterious effects of hydrogen halide thereon at elevated temperatures. Such necessary demands on the system used for synthesis of the methyl halides contribute to the high cost of methyl halide in the marketplace.
U.S. Pat. No. 4,041,087 describes a method for the preparation of halogenated hydrocarbons, including methyl halides, by reacting carbon monoxide, hydrogen and a source of halogen in the presence of a particular catalyst at temperatures from 200.degree. to 1000.degree. C., preferably 200.degree.-700.degree. C. and at pressures from 0.1 to 500 atm, most preferably 1-10 atm. In the examples of preferred embodiments set forth in the patent, temperatures of 270.degree. C. and above are employed. The catalyst is described as one of several specific Group VIII metals or alloys (rhenium, platinun-iridium and platinum-rhenium) in combinations with an acidic inorganic oxide material.
Although the patented method represents a new approach to the preparation of halogenated hydrocarbons, it also requires the utilization of substantially the same rigorous conditions employed in typical prior art methods. As a result, the costs of halogenated hydrocarbons produced according to the patented method remain relatively high.
It is an object of the present invention to provide a method for the preparation of methyl halide and mixtures thereof with halogenated ethanes which can be carried out at much lower temperatures and under milder conditions than utilized heretofore thereby resulting in substantial cost savings.